1. Field of the Invention
The present invention generally relates to the fabrication of integrated circuits, and, more particularly, to the formation of a contact connecting to a buried conductive region formed in a semiconductor substrate.
2. Description of the Related Art
In modern integrated circuits, a huge number of individual circuit elements, such as transistors, resistors, capacitors and the like, are typically formed on a limited chip area, wherein the feature sizes of the individual circuit elements are typically shrunk for every new device generation so as to enhance the functionality of the circuit by improving the performance of the individual circuit elements and by increasing the number of circuit elements provided on a specified chip area. Increasing the number of circuit elements per unit area typically entails an even stronger increase of the number of electrical connections connecting the individual circuit elements in accordance with the design requirements.
In addition to doped semiconductor lines provided as extra layers and metal lines provided in the form of so-called metallization layers, typically so-called buried lines, i.e., buried zones or regions formed in the semiconductor substrate below the surface thereof, may be used as connections between circuit elements and/or circuit regions without requiring the formation of any extra layers above the substrate layer bearing the circuit elements. These buried lines, however, need to be contacted so as to supply any voltage or signals thereto, wherein a photolithography technique is conventionally used that requires the alignment of a corresponding image mask to the buried lines formed in the semiconductor substrate. After exposure and development of the photoresist used during the photolithography step, the corresponding resist mask is then used to form an opening to the buried line by, for instance, anisotropic etch techniques. Subsequently, the opening is filled with an appropriate material, such as a refractory metal, thereby forming a low-ohmic contact to the buried line. The involved photolithography step requiring a precise alignment in order to obtain an optimum conductivity between the contact material and the buried line is, however, time-consuming and thus cost-intensive.
Accordingly, a need exists for a technique that enables the formation of a contact connecting to a buried line with a minimum number of additional process steps and a high degree of compatibility to existing process schemes.